By Beth Miller
Vehicles fueled by diesel lead to substantial carbon emissions that are challenging to decarbonize. In 2022, diesel fuel use made up about one-fourth of total U.S. transportation carbon dioxide emissions and about one-tenth of total energy-related carbon dioxide emissions, according to the U.S. Energy Information Administration.
Joshua Yuan , the Lucy & Stanley Lopata Professor and chair of the Department of Energy, Environmental & Chemical Engineering in the McKelvey School of Engineering at Washington University in St. Louis, and Susie Dai , a MizzouForward Professor of Chemical and Biomedical Engineering at the University of Missouri, and their collaborators at Texas A&M University, have used electrocatalysis of carbon dioxide to create an electro-biodiesel that is 45 times more efficient and uses 45 times less land than soybean-based biodiesel production. Results of their work are published online in Joule Oct. 31.
"This novel idea can be applied to the circular economy to manufacture emission-negative fuels, chemicals, materials and food ingredients at a much higher efficiency than photosynthesis and with fewer carbon emissions than petrochemicals," said Yuan, who began the work with Dai at Texas A&M University. "We have systemically addressed the challenges in electro-biomanufacturing by identifying the metabolic and biochemical limits of diatomic carbon use and have overcome these limits."
The team used electrocatalysis, a type of chemical reaction initiated by electron transfers to and from reactants on surfaces of catalysts, to convert carbon dioxide into biocompatible intermediates, such as acetate and ethanol. The intermediates were then converted by microbes into lipids, or fatty acids, and ultimately became biodiesel feedstock, said Yuan, also director of the National Science Foundation-funded Carbon Utilization Redesign for Biomanufacturing-Empowered Decarbonization (CURB) Engineering Research Center (ERC).
The novel microbial and catalyst process developed by Yuan, Dai and their teams allowed their electro-biodiesel to reach 4.5% solar-to-molecule efficiency for converting carbon dioxide to lipid, which is considerably more efficient than biodiesel [BM1] . Nature photosynthesis in land plants is normally below 1%, where less than 1% of sunlight energy is converted to plant biomass by converting CO2 to diverse molecules for plant growth, Yuan explained.
"The amount of energy diverted to the biodiesel precursor, lipid, is even lower as lipid has high energy intensity," he said. "On the contrary, the electro-biodiesel process can convert 4.5% of solar energy to lipids when a solar panel is used to produce electricity to drive electrocatalysis, which is much higher than the natural photosynthetic process."
To prompt the electrocatalysis, the team designed a new zinc- and copper-based catalyst that produces diatomic carbon intermediates that could be converted into lipids with an engineered strain of the Rhodococcus jostiii (RHA1) bacterium, known to produce high lipid content. This strain also boosted the metabolic potential of ethanol, which could help to prompt conversion of acetate, an intermediate, to the fatty acid.
After developing the novel process, the team analyzed the impact of the process on climate change and found encouraging results. By using renewable resources for the electrocatalysis, the electro-biodiesel process could reduce 1.57 grams of carbon dioxide per gram of electro-biodiesel produced with the by-products of biomass, ethylene and others, giving it the potential for negative emissions. In contrast, conventional diesel production from petroleum produces 0.52 grams of carbon dioxide per gram, and biodiesel production methods produce 2.5 grams to 9.9 grams of carbon dioxide per gram of lipids produced.
"This research proves the concept for a broad platform for highly efficient conversion of renewable energy into chemicals, fuels and materials to address the fundamental limits of human civilization," Yuan said. "This process could relieve the biodiesel feedstock shortage and transform broad, renewable fuel, chemical and material manufacturing by achieving independence from fossil fuel in the sectors that are fossil-fuel dependent, such as long-range heavy-duty vehicles and aircraft."
